The present invention relates to industrial control systems that employ a large number of controlled devices and, more particularly, to industrial control systems which utilize a single board computer (SBC) associated with and for controlling each controlled device.
Many system-type industrial installations, for example, power generating stations, employ a large number of controlled devices for effecting coordinated operation of the overall system. These controlled devices include, for example, motors, pumps, compressors, various types of electrically operated valves, transmissions, instruments, solenoids, relays, and the like. Each of these controlled devices has a particular set of logic function or control signals and/or command sequences that must be effected to ensure proper device operation. These logic function signals and command sequences include, for example, enable signals, stand-by signals, turn-on signals, turn-off signals, run-up and run-down sequences, time delays, emergency stop signals, and various alarm condition signals.
In the past, coordinated control of the various devices has been achieved by manual operation and various types of semi-automatic and automatic control systems including electromagnetic relay systems, hard-wired solid-state logic systems, computer control systems in which the controlled devices are connected to and controlled from a central computer and, more recently, distributed computer control systems in which a single board computer is connected to each controlled device with each computer having a program dedicated to the particular controlled device.
While both types of computer-oriented control systems, that is, the central computer arrangement and the distributed computer arrangement, provide effective system control, a number of drawbacks are associated with the introduction of computer control within a control system.
In a large control system, e.g., a control system for a power generating installation, a substantial programming effort must be undertaken to provide software for each of the controlled devices within the system. In installations using a large central computer, this programming effort is lessened somewhat by the ready availiability of sophisticated high-level program languages that permit a relatively unskilled system controller to structure the necessary control programs. These sophisticated languages oftentimes include subroutines, e.g., query prompters and graphic display subroutines, that assist and guide the system control personnel in structuring the programs.
On the other hand, single board computers are generally programmed in low-level assembly-type languages or machine language codes, and, as a consequence, many system users are reluctant to employ distributed single board computers because of the difficulty in obtaining or training personnel to program the computers. As a practical consequence, system users employing single board computers are dependent upon their computer suppliers or other consultants for these control programs.
Other drawbacks that are associated with distributed single board computer systems are that maintenance personnel, who are not usually trained in programming, must have a large inventory of preprogrammed single board computers with which to conduct "remove and replace" type troubleshooting. Also, the replacement of a defective controlled device with an updated or modified replacement oftentimes requires that the control program within the associated control computer be modified to reflect the updated or modified control function and/or command sequence logic of the replacement device.
The time and cost problems associated with developing a control system having a large number of controlled devices with a single board computer for each device does not normally prevent this type of system from being used in newly designed industrial systems. However, the same time and cost factors can prevent, or at least inhibit, cost effective retrofitting of existing industrial installations with dedicated single board computers because of the time required to identify the logic control functions and control sequences of operating equipment and the downtime that may be required to prepare and test a dedicated program for each single board computer.